The ion acoustic decay instability, and anomalous laser light absorption for the OMEGA upgrade, large scale hot plasma application to a critical surface diagnostic, and instability at the quarter critical density. Final report

It is shown that laser light can be anomalously absorbed with a moderate intensity laster (I{lambda}{sup 2}{approx}10{sup 14} W/cm{sup 2}-{mu}m{sup 2}) in a large scale, laser produced plasma. The heating regime, which is characterized by a relatively weak instability in a large region, is different from the regime studied previously, which is characterized by a strong instability in a narrow region. The two dimensional geometrical effect (lateral heating) has an important consequence on the anomalous electron heating. The characteristics of the IADI, and the anomalous absorption of the laser light were studied in a large scale, hot plasma applicable to OMEGA upgrade plasma. These results are important for the diagnostic application of the IADI

Lasers: The first fifty years

This year marks the 50th anniversary of the invention of the laser. The Optical Society of America is publishing this feature issue to celebrate this auspicious birthday. © 2010 Optical Society of America

Laser-plasma interactions in long-scale-length plasmas under direct-drive National Ignition Facility conditions

Laser-plasma interaction experiments have been carried out on the OMEGA laser system [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] under plasma conditions representative of the peak of a 1.5 MJ direct-drive laser pulse proposed for the National Ignition Facility (NIF). Plasmas have been formed by exploding 18–20 μm thick CH foils and by irradiating solid CH targets from one side, using up to 20 kJ of laser energy with phase plates installed on all beams. These plasmas and the NIF plasmas are predicted to have electron temperatures of 4 keV and density scale lengths close to 0.75 mm at the peak of the laser pulse. The electron temperature and density of the exploding-foil plasmas have been diagnosed using time-resolved x-ray spectroscopy and stimulated Raman scattering, respectively, and are consistent with predictions of the two-dimensional Eulerian hydrodynamics code SAGE [R. S. Craxton and R. L. McCrory, J. Appl. Phys. 56, 108 (1984)]. When the solid-target or exploding-foil plasmas were irradiated with an f/6f/6 interaction beam at 1.5×1015 W/cm2,1.5×1015W/cm2, well above the NIF f/8f/8 cluster intensity of ∼ 2×1014 W/cm2,∼2×1014W/cm2, stimulated Brillouin backscattering (SBS) was found to be completely inhibited. A conservative upper limit of direct-backscattered SRS was found to be ∼5% from the solid targets. SRS and SBS are thus unlikely to have a significant impact on target performance at the peak of the NIF direct-drive laser pulse. © 1999 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70094/2/PHPAEN-6-5-2072-1.pd

Assessment of ion kinetic effects in shock-driven inertial confinement fusion implosions using fusion burn imaging

The significance and nature of ion kinetic effects in D3He-filled, shock-driven inertial confinement fusion implosions are assessed through measurements of fusion burn profiles. Over this series of experiments, the ratio of ion-ion mean free path to minimum shell radius (the Knudsen number, NK) was varied from 0.3 to 9 in order to probe hydrodynamic-like to strongly kinetic plasma conditions; as the Knudsen number increased, hydrodynamic models increasingly failed to match measured yields, while an empirically-tuned, first-step model of ion kinetic effects better captured the observed yield trends [Rosenberg et al., Phys. Rev. Lett. 112, 185001 (2014)]. Here, spatially resolved measurements of the fusion burn are used to examine kinetic ion transport effects in greater detail, adding an additional dimension of understanding that goes beyond zero-dimensional integrated quantities to one-dimensional profiles. In agreement with the previous findings, a comparison of measured and simulated burn profiles shows that models including ion transport effects are able to better match the experimental results. In implosions characterized by large Knudsen numbers (NK3), the fusion burn profiles predicted by hydrodynamics simulations that exclude ion mean free path effects are peaked far from the origin, in stark disagreement with the experimentally observed profiles, which are centrally peaked. In contrast, a hydrodynamics simulation that includes a model of ion diffusion is able to qualitatively match the measured profile shapes. Therefore, ion diffusion or diffusion-like processes are identified as a plausible explanation of the observed trends, though further refinement of the models is needed for a more complete and quantitative understanding of ion kinetic effects

Using Inertial Fusion Implosions to Measure the T + 3He Fusion Cross Section at Nucleosynthesis-Relevant Energies

Light nuclei were created during big-bang nucleosynthesis (BBN). Standard BBN theory, using rates inferred from accelerator-beam data, cannot explain high levels of [superscript 6]Li in low-metallicity stars. Using high-energy-density plasmas we measure the T([superscript 3]He,γ)[superscript 6]Li reaction rate, a candidate for anomalously high [superscript 6]Li production; we find that the rate is too low to explain the observations, and different than values used in common BBN models. This is the first data directly relevant to BBN, and also the first use of laboratory plasmas, at comparable conditions to astrophysical systems, to address a problem in nuclear astrophysics.United States. Department of Energy (DE-NA0001857)United States. Department of Energy (DE-FC52-08NA28752)United States. Department of Energy (DEFG02-88ER40387)United States. Department of Energy (DE-NA0001837)United States. Department of Energy (DE-AC52- 06NA25396)Lawrence Livermore National Laboratory (B597367)Lawrence Livermore National Laboratory (415935- G)University of Rochester. Fusion Science Center (524431)National Laser User’s Facility (DE-NA0002035)National Science Foundation (U.S.). Graduate Research Fellowship Program (Grant 1122374)Los Alamos National Laboratory. Laboratory Directed Research and Development Program (20150717PRD2

Saturation of the Two-Plasmon Decay Instability in Long-Scale-Length Plasmas Relevant to Direct-Drive Inertial Confinement Fusion

Measurements of the hot-electron generation by the two-plasmon-decay instability are made in plasmas relevant to direct-drive inertial confinement fusion. Density-scale lengths of 400 {micro}m at n{sub cr}/4 in planar CH targets allowed the two-plasmon-decay instability to be driven to saturation for vacuum intensities above ~3.5 x 10{sup 14} W cm{sup -2}. In the saturated regime, ~1% of the laser energy is converted to hot electrons. The hot-electron temperature is measured to increase rapidly from 25 to 90 keV as the laser beam intensity is increased from 2 to 7 x 10{sup 14} W cm{sup -2}. This increase in the hot-electron temperature is compared with predictions from nonlinear Zakharov models

Efficient Coupling of 527 nm Laser Beam Power to a Long Scalelength Plasma

We experimentally demonstrate that application of laser smoothing schemes including smoothing by spectral dispersion (SSD) and polarization smoothing (PS) increases the intensity range for efficient coupling of frequency doubled (527 nm) laser light to a long scalelength plasma with n{sub e}/n{sub cr} = 0.14 and T{sub e} = 2 keV

Exploration of the Transition from the Hydrodynamiclike to the Strongly Kinetic Regime in Shock-Driven Implosions

Clear evidence of the transition from hydrodynamiclike to strongly kinetic shock-driven implosions is, for the first time, revealed and quantitatively assessed. Implosions with a range of initial equimolar D[superscript 3]He gas densities show that as the density is decreased, hydrodynamic simulations strongly diverge from and increasingly overpredict the observed nuclear yields, from a factor of ∼2 at 3.1  mg/cm[superscript 3] to a factor of 100 at 0.14  mg/cm[superscript 3]. (The corresponding Knudsen number, the ratio of ion mean-free path to minimum shell radius, varied from 0.3 to 9; similarly, the ratio of fusion burn duration to ion diffusion time, another figure of merit of kinetic effects, varied from 0.3 to 14.) This result is shown to be unrelated to the effects of hydrodynamic mix. As a first step to garner insight into this transition, a reduced ion kinetic (RIK) model that includes gradient-diffusion and loss-term approximations to several transport processes was implemented within the framework of a one-dimensional radiation-transport code. After empirical calibration, the RIK simulations reproduce the observed yield trends, largely as a result of ion diffusion and the depletion of the reacting tail ions.United States. Dept. of Energy (Grant DE-NA0001857)United States. Dept. of Energy (Grant DE-FC52-08NA28752)University of Rochester. Fusion Science Center (5-24431)National Laser User’s Facility (DE-NA0002035)University of Rochester. Laboratory for Laser Energetics (415935-G)Lawrence Livermore National Laboratory (B597367